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Home , Autonomic ganglion, Node of Ranvier, Pseudounipolar neuron

Introduction Remember those four Basic Tissues? Here they are again:

1. Epithelial tissue 2. Connective tissues 3. Muscle tissue 4.

During this lab you will learn about the fourth Basic Tissues: Nervous Tissue.

Anatomically the is divided into the:

i. (CNS)- the brain and . ii. Peripheral Nervous System (PNS) - peripheral /ganglia outside the CNS.

Functionally the nervous system consists of the:

i. Somatic nervous system - which controls voluntary activities. ii. Visceral/ - which controls involuntary activities.

During this lab you will concentrate on the general appearance of nervous tissue and, in particular focus on recognizing peripheral nerves in histological sections. You will learn more about the organ components of the CNS (brain and spinal cord) in future labs.

Learning objectives and activities Using the Virtual Slidebox:

A IDENTIFY NERVOUS TISSUE & ITS CELLS Recognize nervous tissue in histological sections and discuss the organization/function of the cells present. B IDENTIFY PERIPHERAL NERVES Examine the features of peripheral nerves in both longitudinal and cross section that allow you to identify them in tissue sections. C IDENTIFY GANGLIA Differentiate between sensory and autonomic (sympathetic/parasympathetic) ganglia.

D TEST YOUR SKILLS Complete the self-quiz to test your understanding and master your learning. IDENTIFY NERVOUS TISSUE & ITS CELLS

Despite its complexities, the nervous system is composed entirely of two cell types: a network of cells () that transmit signals throughout the nervous system and the glial cells that support them.

Neurons

Examine Slide 1 (16) to investigate the basic structure of a ii

i. Cell body (perikaryon). Most cell bodies are located in the central nervous system (brain and spinal cord) or in ganglia of the peripheral nervous i system. They contain darkly stained granules called Nissl bodies which are the ribosomes used to manufacture iii neurotransmitter in the cell.

iv ii. Dendrites extend from the cell body. These are short, highly branched structures that receive nerve impulses from other neurons. Nissl bodies can be seen extending into the dendrites.

iii. Nucleus and nucleolus Neurons have a large nucleus with prominent nucleolus. The ribosomes seen in the cell body are assembled in the nucleolus.

iv. hillock and axon The is where the axon branches from the cell body. It contains the Golgi apparatus and is therefore devoid of Nissl bodies. The axon is a single 'fiber' that transmits impulses. Most neurons have an axon surrounded by fat – the sheath – which assists propagation of electrical impulses along the axon. There are three basic classes of neuron (they all look the same so their location is key)

i. Multipolar neurons Located in CNS Located in PNS Have multiple dendrites and a long axonal process. They convey either somatic motor or visceral/autonomic Skeletal muscle motor information from the CNS.

Examine the following slides Somatic motor to see examples of multipolar neurons: Pre-ganglionic Slide 1 (16) : somatic motor Autonomic Slide 2a (19) : somatic motor Smooth muscle (e.g. vessels or Slide 3a (21) : visceral motor digestive tract)

Post-ganglionic Visceral motor ii. Pseudounipolar neurons Have one axon that divides close to the cell body to form two long axonal branches. They convey sensory information to the CNS and their cell bodies are located within the dorsal root ganglion (or cranial nerve Visceral and ganglia). somatic sensory

Examine Slide 4a (20) to see pseudounipolar (sensory) neurons in a dorsal root ganglion.

iii. Bipolar neurons Have one axon and one . They convey special sensation to the CNS.

Examine Slide 5 (82) to see Special sense bipolar neurons in the retina. Glial cells

Glial cells support and protect the neurons.

i. In the CNS There are many different types of glial cell: - - the equivalent of Schwann cells in the CNS - - specialized macrophages that protect CNS neurons - - regulate chemical environment in CNS (blood-brain barrier) - ependymal cells - line ventricles of brain and central canal of spinal cord

Together they form the ‘’ of the CNS known as ‘’.

With the exception of ependymal cells it is very difficult to specifically identify the different types of glial cell within the central nervous system without specific stains. Therefore you will not be asked to do this.

Explore Slide 2b (19) to see glial cells, neuropil and ependymal cells in the CNS.

ii. In the PNS, There are two types of glial cell: - Schwann cells - form the myelin sheath surrounding the axon of the neuron - satellite cells - surround and support neuron cell bodies located in the PNS.

Explore Slide 3b (21) and Slide 4b (20) to see Schwann cells and satellite cells in the PNS (ganglia). IDENTIFY PERIPHERAL NERVES

In a typical peripheral nerve, individual nerve are bundled together to form a series of layers v. surrounded by connective tissue. These are best seen vi. in cross sections through nerves. iv.

Identify features of a peripheral nerve in both the iii. longitudinal AND cross section shown in Slide 6 (17)

i. External coat of dense irregular connective tissue.

ii. ii. Connective tissue surrounding individual axon bundles that are called fascicles.

iii. Thin connective tissue layer surrounding each individual axon and its myelin sheath.

iv. Myelin sheath The fatty sheath formed by the surrounding the axon.

v. Axon i. The long process of an individual neuron that extends from the cell body. vi. A Na+ channel rich ‘gap’ between adjacent Schwann cells that allows rapid propagation of impulses along an axon. These are only visible in longitudinal sections of nerves. IDENTIFY GANGLIA

Ganglia are nodular masses of connective tissue and neuron cell bodies surrounded by supporting glial cells (satellite cells). There are two types of ganglia in the PNS: i. Sensory ganglia Located in CNS Located in PNS Collections of cell Dorsal root ganglion bodies that: Satellite cells - convey afferent impulses towards the CNS - are associated with (cranial ganglia) and the spinal cord (dorsal root ganglia) - are tightly clustered and bounded by a CT capsule Examine Slide 4a (20) again to identify the key features - have large central located nuclei of a sensory ganglion and ensure you can differentiate and prominent nucleolus. this from an . - are surrounded by supportive satellite cells (glial cells).

Located in CNS Located in PNS ii. Autonomic ganglia Sympathetic ganglion Collections of multipolar, post ganglionic (in sympathetic chain) neuron cell bodies that: - control activity of smooth muscle, glands and cardiac

rhythm Satellite cells - can be located close to the spinal sympathetic cord = (see Slide 3a) Parasympathetic - can be located close to/within an ganglion organ = parasympathetic (see (in wall of organ) Slide 7). - are scattered and bounded by a CT capsule Satellite cells - have small nuclei with an eccentric nucleolus. - are each surrounded by Compare Slide 3a (21) of the sympathetic chain and supportive satellite cells (glial Slide 7 (54) which contains a parasympathetic ganglion cells) to identify the key (differentiating) features of - may contain lipofuscin granules autonomic ganglia. Ensure you can tell them both apart from sensory ganglia. TEST YOUR KNOWLEDGE

You must be able to identify the following types of nervous tissue and their associated histological features in a variety of tissues:

Neurons Multipolar Pseudounipolar Bipolar Cell body (perikaryon) Nissl bodies Dendrites Axon Axon hillock Nucleus Nucleolus

Glial cells Glial cells (in CNS: do not need to be specific) Ependymal cells (in CNS) Satellite cells (in PNS) Schwann cells (in PNS)

Peripheral nerve (in longitudinal and cross section) Epineurium Perineurium Endoneurium Axon Myelin sheath Schwann cell Node of Ranvier

Ganglia Sensory/Dorsal root ganglion Autonomic/sympathetic ganglion Autonomic/parasympathetic ganglion Lipofuscin Satellite cells